You can check the IP with the interface :
When u rcv a packet from the external interface, deny packets which come
with local IP (192.168.XXX.XXX or 172.16.XXX.XXX or others as non
routing IP : 10.0.0.10,etc.)
U can also just allow locals IP (if people don't have to send mail out
from your LAN)
And then, if you use a SMTP relay, just add its @ and deny others from
external interface.
Another good thing is to control the TCP/IP sequence and to check the
tcp hand shake (--tcp-flags SYN,ACK,RST SYN)
maybe, u'll want to add:
iptables -A INPUT -m state --state NEW,RELATED -p tcp --syn -j ACCEPT
iptables -A INPUT -m state --state ESTABLISHED -p tcp ! --syn -j ACCEPT
I hope it was what u need.
Pierre BETOUIN
Le sam 23/11/2002 � 07:27, Erick Arturo Perez Huemer a �crit :
> I am about to install a RedHat 8.0 box with iptables to act as our
> firewall for our internal network that consists of 20 machines.
>
> Besides doing a -j drop on our external interface when receives a
packet
> with source equal to our internal network, what other measures we have
> to take?
>
> We do host an SMTP server but nothing else. I have read about blocking
> 10.x.x.x addresses but also read that "some" routers/sites use those
> addresses. Any anti-DoS rules? More settings?
>
> Or maybe a link to a site that offers suggestion for proper firewall
> configurations....
>
> Thanks in advance,
>
> Erick.
--
Pierre BETOUIN <[EMAIL PROTECTED]>
